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EUVEUV LITHOGRAPHYLITHOGRAPHY2005 EUVL Symposium, 7-9 November 2005ASET, Takeichi 1

High-precision (<1ppb/℃) optical heterodyne interferometric dilatometer for

low thermal expansion materials

Yoshimasa Takeichi, Iwao Nishiyama Association of Super-Advanced Electronics Technologies

(ASET)EUV Process Technology Research Laboratory

Naofumi YamadaNational Institute of Advanced Industrial Science and Technology

(AIST) National Metrology Institute of Japan（NMIJ）

EUVEUV LITHOGRAPHYLITHOGRAPHY2ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005

Acknowledgement

This work was supported by the New Energy and

Industrial Technology Development Organization (NEDO).


Outline

1. Background CTE characteristics, CTE metrology

2. Goal Target performance of dilatometer

3. Methodology Principle & design of the dilatometer

4. Results Evaluation of the performance of the dilatometer

5. Summary


1. Background


（Change in substrate temperature）

Exposure

Before After

Expansion(Shrinkage)

Background (1): CTE of EUVL Mask Substrate

Mask ｓtage

source

λ:13nm

Waferstage

Illumination Optics

Projection Optics λ：13.5 nm

Reflective Optics

ML,Reflectance :<70%)

Exposure under vacuum

Exposure deforms mask.

Configuration of EUVL system

CTE: Coefficient of Thermal Expansion

Difficult requirement to meet

No commercial dilatometer that meets EUVL requirements

Obstacle to the development of LTEMs

SEMI standards (Class A)0±5 ppb/ﾟC（19-25ﾟC）1ppb = 0.1nm (@10cm)

Strong demand for a metrology that meet EUVL

requirement


Background (2): Metrology Development Project

Metrology andpatent ownership

EUVL technologyLTEM developer

Metrology user

Research organizationsLTEM suppliers

DevelopmentDevelopmentteamteam

Equipment supplierEquipment supplierOptical heterodyne interferometer,

Thermal control technique

SpecificationsPerformance

evaluation

Manufacture of equipment

Equipment design


2. Goal


Goal and targets

Overall Goal• To establish a CTE metrology tailored to meet EUVL

requirements and help bring EUVL closer to the stage of practical use

Target

• Resolution: 1 ppb/ﾟC or less

• Repeatability(σ): 1 ppb/ﾟC or less

• Making practical dilatometer: marketable

• Metrology standardization


3. Methodology


AOM

AOM

APD1

He-Ne laser

Spec

imen

Reflector

PBS

Referencelight

Measurementlight

Light frequency 1

Light frequency 2

APD2

Change in length due to change in temperature

Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

AOM

AOM

APD1

He-Ne laser

Spec

imen

Reflector

PBS

Referencelight

Measurementlight

Light frequency 1

Light frequency 2

APD2


Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

Phase difference between APD1 and APD2 at T1：（ φAPD2 -φAPD1）T1

Phase difference between APD1 and APD2 at T2：（ φAPD2 -φAPD1 ）T2

( )λπφφ L

APDAPDΔ

=−Δ2

12

Change in phase difference between T1 and T2：

Methodology (1): Principle of Measurement

ΔL：Change in length

(Quadruple - sensitivity)

Optical heterodyne interferometry

Intensity of superimposed light

Electric field intensity

( )1111 2cos φπ += tfaE

( )2222 2cos φπ += tfaE

221 EEI +=

{ }φπ Δ+++

= tfaaaab2cos2

2 21

22

21

( ) ( ){ }212121

22

21 2cos2

2φφπ −+−+

+= tffaaaa


APD2

AOM APD1

Spec

imen

Reflector

PBS

Referencelight

Measurementlight

Light frequency 2


Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

AOM

AOM

APD1

He-Ne laser

Spec

imen

Reflector

PBS

Light frequency 1

Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

Methodology (1): Optical Path of the Dilatometer


AOM

AOM

APD1

He-Ne laser

Spec

imen

Reflector

PBS

Referencelight

Measurementlight

Light frequency 1

Light frequency 2

APD2


Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

AOM

AOM

APD1

He-Ne laser

Spec

imen

Reflector

PBS

Referencelight

Measurementlight

Light frequency 1

Light frequency 2

APD2


Vacuum chamber

Ther

mal

con

trol b

lock

Ther

mal

con

trol b

lock

Phase difference between APD1 and APD2 at T1：（ φAPD2 -φAPD1）T1

Phase difference between APD1 and APD2 at T2：（ φAPD2 -φAPD1 ）T2

( )λπφφ L

APDAPDΔ

=−Δ2

12

Change in phase difference between T1 and T2：

Methodology (1): Principle of Measurement

ΔL：Change in length

(Quadruple - sensitivity)

Optical heterodyne interferometry

Intensity of superimposed light

Electric field intensity

( )1111 2cos φπ += tfaE

( )2222 2cos φπ += tfaE

221 EEI +=

{ }φπ Δ+++

= tfaaaab2cos2

2 21

22

21

( ) ( ){ }212121

22

21 2cos2

2φφπ −+−+

+= tffaaaa


Methodology (2): To Meet EUVL Requirement

Determination of sample length

Determination of change in sample length due to thermal expansion

Stability of thermo control and determination of temperature

This term has a large influence.

This term has little influence.

This term has little influence.

Consideration of uncertainty factors

TLL

Δ⋅

Δ=

1

0

α

( ) ( ) αδδαδδαTLsp

total TT

TLL

LL

⎥⎦⎤

⎢⎣⎡ΔΔ

+Δ⎥

⎦

⎤⎢⎣

⎡ Δ+⎟⎟

⎠

⎞⎜⎜⎝

⎛=

1

00

0

α：low


Sample inclination prevention ・ Thermal isolation・ Thermal control・ LTEM pedestal

Vibration isolation・ Stone plate・ Vibration isolation table

Compact interferometer

Methodology (3): KEY Design Consideration

Thermal-shield

Stone plateVibration isolation table

interferometer

Frame

Water

sample

LTEM

Inver

Peltier device

Structure of dilatometer

How to reduce magnitude of uncertainty factors affecting ΔL measurement

Frequency-stabilized laser

Design guidelines


Methodology (4): Design Guideline

Pertier　Device

Con

stan

t tem

pare

ture

blo

ckradiation radiation

conduction

Con

stan

t tem

pare

ture

blo

ck

conduction

Configuration of thermo-control system

How to reduce magnitude of uncertainty factors affecting ΔT measurement

To achieve uniform temperature distribution in sample

・ Employment of two heat sources Efficiency: Constant temp. blocksUniformity: Peltier device


Methodology (5): Practical Dilatometer, Sample

Equipment supplier:

Reference

Displacement

Optical path

Arrangement of laser spot

CTE-01


4. Results


Evaluation Items

• Determination of measurable range of CTE and types of materials that could be measured

• ReproducibilityRepeatability (Static) : Reproducibility obtainable from measurements of the same sample without moving it .Resetability (Dynamic) : Reproducibility obtainable from measurements involves changing the sample

• Accuracy of measurements: Under evaluation


Results (1): Measurable CTE range and materials

• Alumina

• SiC

• Silica glass

• Ti-doped silica glass (LTEM)

• Glass ceramics (LTEM)

CTE-01 can handle a wide variety of materials

Measurable CTE range: from ppm/°C to ppb/°C

several ppm/ °C

hundreds ppb/ °C


-700

-500

-300

-100

100

0 10 20 30 40 50 60 70 80

Time [hr]

Phas

e D

iffer

ence

[de

g]

18.0

20.0

22.0

24.0

26.0

0 10 20 30 40 50 60 70 80

Time [hr]

Avg

. tem

pera

ture

[℃

]Change in sample temperature

Change in phase difference176

88

0

-88

-176 Cha

nge

in S

ampl

e Le

ngth

[ nm

]

Results (2): Measured CTE of Silica Glass


Results (2): Measured CTE of Silica Glass

Results of measurement ｆｏｒ CTE of silica glass

[ppm/ﾟC]

T1 T2 Meas.1 Meas.2 Δ (Meas.2-Meas.1)

19 22 0.460 0.464 0.004

22 25 0.470 0.471 0.001

These values tell us that the measurement reproducibility is about several ppm per degree.


-30

-20

-10

0

10

20

30

0 10 20 30 40 50 60 70 80 90 100 110 120

Time [hr]

Phas

e diff

eren

ce [d

eg.]

Results (3): Measured CTE of Ti-doped silica glass

18

20

22

24

26

0 10 20 30 40 50 60 70 80 90 100 110 120

Time [hr]

Avg

. tem

pera

ture

[ ℃]

13.2

0

-13.2

Change in sample temperature

Change in phase difference

Cha

nge

in S

ampl

e Le

ngth

[ nm

]


Results (3): Measured CTE of Ti-doped silica glass

Results of measurement for CTE of LTEM

[ppb/ﾟC]

T1 T2 Meas.1 Meas.2 Δ (Meas.2-Meas.1)

19 22 -19.95 -19.42 0.53

22 25 -13.06 -13.88 -0.83

19 25 -17.32 -17.68 -0.36

These values indicate that the measurement reproducibility is less than 1 ppb per degree.


Results (4): Reproducibility of Measurements

-20-10

01020304050

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102

Time [hr]

Phas

e D

iffer

ence

[de

g]

(a)

18.0

20.0

22.0

24.0

26.0

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102

Time [hr]

Tem

para

ture

(Ave

rage

) [ ℃

] (b)Change in sample temperature

Change in phase differencea

a



Calculated CTE values (Test No.1)

Average: -26.8 ppb/°C , σ: 0.80 ppb/°C



Repeatability

Resetability

[ppb/ﾟC]

Repeatability (Static) : reproducibility obtainable from measurements of the same sample

without moving it .

Resetability (Dynamic) : reproducibility obtainable from measurements involves changing the

sample.

Reproducibility of measurements

ΔCTE: ±0.85 ppb/°C

σ: 0.80 ppb/°C


Results (5): Case of CTE Measurements

Tuesday, November 8

Development of Zero Expansion Glass for EUVL Substrate


Results (5): Case of CTE Measurements


5. Summary


Summary・ An optical heterodyne interferometric dilatometer (CTE-01)

tailored to meet EUVL requirements has been developed.

・The CTE-01 can handle a wide variety of materials, including LTEMs.

・Reproducibility of dataRepeatability, σ: < 1 ppb/°CResetability, ΔCTE: < ±1 ppb/°C

These values meet the target specifications.

・We confirm that the CTE-01 will be useful for the precise measurement of the CTEs of EUVL-grade LTEMs.

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